Butter a large (11X17-inch) rimmed baking sheet or two 9X13-inch pans. Set aside.

In a large saucepan over medium heat, melt the butter. Add the marshmallows and stir until melted and smooth. Remove from the heat and stir in the rice krispies. Press the mixture into the prepared pan(s) and set aside to cool for about an hour.

Using a 2 to 3-inch heart-shaped cookie cutter, press the cutter into the cooled rice krispie treats, removing the heart-shaped treats to a wax paper or parchment paper-lined baking sheet or work space. If you minimize space between the hearts, you should be able to cut out right around 24 hearts. Feel free to do what you like with the extra scraps (we had no trouble coming up with a solution).

In a microwave-safe bowl, melt 12 ounces chocolate chips on 50% power for one minute. Stir. Continue this process until the mixture is melted and smooth but not overheated.

If desired, push a cookie or lollipop stick into the bottom of the rice krispie treats (optional). Holding one side of the rice krispie heart (or using the stick as a handle), dip half of the rice krispie treat into the melted chocolate and then transfer to the wax paper or parchment paper. I alternated between dipping the top half of the treat or either side of the treat. While the chocolate is still warm on the rice krispie heart, sprinkle the festive Valentine (or other) sprinkles onto the chocolate. Let the treats cool completely and the chocolate harden before serving, about 1-2 hours.

Cover in an airtight container to store (they are best eaten within 24 hours).